EP2480911B1 - Method and device for measuring a contour of the ground - Google Patents

Description

The invention relates to a method for measuring a soil profile by means of a mounted on a vessel transmitting and receiving arrangement referred to in the preamble of claim 1 and a device for carrying out the method according to claim 6.

The invention finds application, inter alia, in the measurement of a soil profile within a predetermined underwater area or in the search for sunken objects. If the underwater area is illuminated in front of the vessel, this serves among other things for collision avoidance and / or navigation.

In order to obtain a detailed object detection, a high angular resolution of the receiving arrangement is necessary. This is conventionally achieved by means of a receiving arrangement with a plurality of transducers and a downstream direction generator. The direction generator processes the respective received signals of the transducers in such a way that the receiving arrangement spans a fan of a multiplicity of directional characteristics or beams pivoted relative to one another in a fixed underwater area. In this case, the receiving arrangements can be formed, for example, as a linear array or conformal arrays or horseshoe or cylindrical bases. DE 199 59 014 A1 shows, for example, a method for determining depth values of a water body with a fan slot. Here, sound velocities are measured for each lot fan for a sequence of fan beams and the depth and storage values are calculated therefrom. Since the resolution of these transducer arrays corresponds to the beam width, however, a very high cost arises for a sufficiently accurate angular resolution.

In addition to these methods by means of a converter array as a receiving arrangement whose resolution is limited by the type of receiving arrangement, so-called. High-resolution methods for angle determination are also known. These methods include, among others, the MUSIC (Multiple Signal Classification) method. However, the accuracy of the results is also dependent on the number of transducers of the receiving arrangement in these methods. The more transducers the receiving arrangement has and the longer the processing signal block is, the more accurate the results. The disadvantage of these methods is also their high computational complexity, which makes it difficult to use in real-time systems.

Alternatively, it is known to carry out the measurement of the soil profile by means of phase evaluation of the sound waves received by the transducers. DE 10 2005 041 390 A1 shows a method for generating a sonar image. For this purpose, a sonar carried by a watercraft is used, which has a transmitting antenna for emitting sound pulses and a receiving antenna with a plurality of hydrophones. In one embodiment, the generation of a three-dimensional sonar image using an interferometric measurement technique is disclosed. For this purpose, a second, preferably identical to the first trained receiving antenna is needed. A depth value to be determined is determined by correlation of the received signals of both receiving antennas.

In the article " Signal Processing Strategies for a Bathymetric Side Scan Sonar "by Philip N. Denbigh of IEEE Journal of Oceanic Engineering, 19 (3): 382-390, July 1994 Principles of direct phase measurement in interferometric systems are described in more detail. Such an interferometric technique requires a second transducer independent of the first one. This provides a further received signal, which provides a time-delayed signal to the first transducer by the different distances to the object. However, if the distance of the transducers is a multiple of the wavelength of the received sound waves, the measured phase shift, which is between 0 and 2π, indicates a set of possible reception angles. Such Ambiguity in angle determination is conventionally avoided by the use of multiple transducers located at a suitable distance.

DE 1 548 452 A shows a method for determining contour lines of the seabed. The searched contour lines can be recorded directly by a special arrangement of the transceiver. According to this arrangement, the transmitting and receiving devices are arranged at such a distance from each other that, after reflection at the seabed, waves received by the same transmitter and received by two mutually remote receivers are received in phase. The disadvantage here is the need to maintain a Certain arrangement ratio, which always has to be adjusted. However, using multiple transducers also disadvantageously increases costs.

The invention is therefore based on the problem to provide a cost-effective method for measuring a soil profile, which provides clear measurement results by means of phase evaluation.

The invention solves this problem by the features of a method according to claim 1 and by a corresponding device with the features of claim 6.

Initially, pulse-shaped sound signals are emitted in a directionally directed manner by means of a transmission arrangement. In this case, the transmitting arrangement has a very narrow directional characteristic, so that only the echoes of a narrow ground strip are received.

In a plurality of N soundings from predetermined positions with different aspect angles and distances from the bottom profile, a sound signal is radiated into the underwater area and its reflected portions are received by the receiving arrangement, wherein the receiving arrangement advantageously manages with two individual transducers. The survey of the soil profile takes place on the basis of the received signals of the two transducers using a pure phase evaluation and a subsequent density analysis of the measured values.

Depending on the distance of the transducers of the receiving arrangement and the frequency or the wavelength of the emitted sound signal, a pure phase evaluation provides ambiguous results. The method according to the invention initially does not consider this ambiguity in the determination of the angle.

The multiple measurement of the soil profile resulting from the ambiguous results of the phase evaluation from different positions of the transmission arrangement is used to unambiguously determine the soil profile using a density analysis. In this case, a phase difference between two received signals at a plurality of predetermined sampling times and the N Lotungen from different positions depending on the distance of the transducer of the receiving device provides several ambiguous path differences. From these ambiguous gait differences, it is possible to determine for these sampling times and for the N placements associated incident angles and incidence coordinates. For the sampling times and the N placements, in each case a data density in a predetermined area containing the incidence coordinate is determined for the ambiguous incidence coordinates. In the area where the true ground point is located, the density of the measured values increases. The locations of the further ambiguous landing coordinates that result from the phase evaluation have a lower data density and are marked as invalid. The method of the invention thus provides a method for determining which is the true landing coordinate on the soil profile.

The inventive method has the advantage that despite an aforementioned ambiguity of the angle determination when using a receiving arrangement with at least two transducers unique measurement results can be achieved by the measurement of the soil profile from different positions with different aspect angles and distances from the soil profile takes place and then a density analysis of the measured data is performed.

In a further embodiment of the invention, the device according to the invention has the advantage that it can be produced using a receiving arrangement with only two individual transducers. The inventive method also provides clear measurement results of the soil profile, when the distance of the transducer is greater than half the wavelength of the received signal or the received sound waves. By virtue of the preferably small dimension, such a receiving arrangement can also be carried, for example, by small, autonomously operating or remotely controlled underwater vehicles.

In a further embodiment of the invention, a transducer array is used as receiving device. If the transmission arrangement is not designed in such a way that directed emission of sound signals into an underwater area is possible or if the transmission arrangement has a directional characteristic which is broad in the forward direction of the vessel, then a reception arrangement with a multiplicity of transducers and a downstream directional generator or beamformer is provided creates a variety of fan-spanned beams the underwater area, the advantage of increasing the resolution of the sonar system according to the beam width.

In a further embodiment of the invention, the regions in which the density of the measured values is determined correspond to surface elements having a predetermined size. These surface elements are the same size for all impact coordinates. Advantageously, the size is determined according to the computational effort and the required resolution.

In a further embodiment of the invention, the N mutually different positions of the N Lotungen be predetermined by a forward movement of the transmitting and receiving device. Preferably, this corresponds to a forward movement of the watercraft. The advantage of such an embodiment is that the transmitting and receiving arrangements can be rigidly mounted instead of in a pivotable embodiment.

Fig. 1

eine schematische Darstellung eines Wasserfahrzeugs mit dem zu erfassenden Unterwasserareal,

Fig. 2 A-B

eine schematische Darstellung des Sonarsystems,

Fig. 3

eine schematische Darstellung der Empfangsanordnung,

Fig. 4

ein Flussdiagramm des erfindungsgemäßen Verfahrens,

Fig. 5

eine schematische Darstellung einer auf die Wandler treffenden Schallwellenfront und

Fig. 6

ein Blockschaltbild der erfindungsgemäßen Vorrichtung zum Ausführen des Verfahrens.

Further advantageous embodiments will become apparent from the dependent claims and from the closer explained with reference to the accompanying drawings embodiments. In the drawing show:

Fig. 1

a schematic representation of a watercraft with the underwater area to be recorded,

Fig. 2 AB

a schematic representation of the sonar system,

Fig. 3

a schematic representation of the receiving arrangement,

Fig. 4

a flow chart of the method according to the invention,

Fig. 5

a schematic representation of an incident on the transducer sound wave front and

Fig. 6

a block diagram of the inventive device for carrying out the method.

Fig. 1 shows a schematic representation of a moving in a sea area watercraft 2 with a forward-looking sonar system 4. This sonar system 4 has a transmitting and receiving arrangement and an associated signal processing for data acquisition of a soil profile 6. However, the invention is not limited to the embodiment by means of a Forward-looking sonar systems 4 limited. Furthermore, for example, a sound radiation over the stern of a watercraft 2 is possible.

In Fig. 1 In addition, the measurement geometry with the distance r of a ground point to the sonar system 4 is shown. The distance r can be determined over the duration of the reflected sound signal. The sound impulse needs one certain time until it reaches the ground, is reflected and arrives after a further period of time at the receiving arrangement. Because of this measurable total running time, the distance r of an object or of the ground point can be determined by means of the known speed of sound.

Furthermore, a reference height H and the aspect angle φ in the perpendicular direction to the sonar system 4 are shown.

To measure the soil profile 6, sound signals directed by the sonar system are directed into an underwater area 8 and the reflected sound waves 10 are received at a multiplicity of ground points (x, y, z). In this case, the sonar system 4 has a very strong bundled sound radiation transversely to the direction of travel and a wide directional characteristic in the vehicle longitudinal direction. As a result, only the echoes of a narrow strip of ground are received.

The extent of the illuminated underwater area 8 is dependent on the formation of the sonar system 4, which in Fig. 2 is shown in detail.

Fig. 2 AB show a schematic representation of the sonar system 4. In Fig. 2 A is a side view of the sonar system 4 and shown in FIG Fig. 2 B a plan view of the same arrangement.

The transmitting arrangement 20 has a multiplicity of transducers arranged on an antenna carrier, which transmit directed sound signals in the form of a transmitting team 22 into a predetermined underwater area 8. The resulting transmission beam 22 in the form of an ellipse has a length 24 and a width 26 dependent on the opening angle of the directional characteristic associated with the transmission arrangement.

From this transmission arrangement 20 is successively with a plurality of N Lotungen from predetermined positions P ₁ , P ₂ , P ₃ , P ₄ , ..., P _N with different aspect angles φ _N and distances r _N to the bottom profile 6 a Sound signal sent into the underwater area 8, wherein the different positions P ₁ , P ₂ , P ₃ , P ₄ , ..., P _{N of} the N Lotungen preferably result from the forward movement of the watercraft 4. Alternatively, it is conceivable to mount the sonar system 4 pivotably on the watercraft 2 in order to obtain the different positions P ₁ , P ₂ , P ₃ , P ₄ , ..., P _{N of} the N plumbs directly by means of a corresponding movement of the sonar system 4 produce. The portions of the sound signal reflected by the bottom profile 6 within the underwater area 8 are received via the receiving arrangement 28, which in Fig. 3 is shown in detail.

Fig. 3 shows a schematic representation of the receiving assembly 28. In order to determine in addition to the distance r and a height h of the soil profile 6, a receiving device 28 is required with at least two different converters. In this embodiment of the invention, the receiving arrangement 28 consists of two individual transducers A and B, as shown in FIG Fig. 3 are shown. They have a distance 30 from one another, which is greater than half the wavelength λ of the output from the transmitting device 20 sound signal. This small positional shift of the transducers A and B results in significant differences in transit time of the received signal, which can be precisely determined on the basis of phase measurements.

However, it is nevertheless possible to use an existing transducer base from which two transducers are picked out. Likewise, the inventive method with two transducer arrays, which according to one another Fig. 2 are arranged feasible. If it requires the design of the watercraft 2, the transducers can also be arranged slightly offset. However, the geometry of the receiving arrangement 28 must be taken into account accordingly in a signal processing of the received signals.

The converter A supplies a received signal, which is delayed in time by the different distances r _A and r _B to the ground point x ₀ with respect to the transducer B. The reflected from the point x ₀ portions of the transmitted sound signal first reach the transducer B and to Δ t delays the converter A. From the phase difference between the associated reception signals can be a height h determined, which is based on the reference height H in the perpendicular direction below the receiver assembly 28. The calculation is performed from the geometry of the measuring arrangement: $$H=H-r_B\cos {\theta }_1$$

Fig. 4 shows a flowchart for describing an embodiment of the method sequence according to the invention, which is based on a multiple measurement of soil elements from different distances r _N and aspect angles φ _N. For this purpose, after an initialization in block 36, first a count variable i in block 38 is assigned the value 1.

In order to measure the soil profile, a sound signal is emitted in accordance with block 40 from a predefined position P ₁ by means of the transmission arrangement 20 into an angular range, preferably narrow in the pre-horizontal direction and wide in the vertical direction.

The sound waves reflected from the ground or object are received by two transducers A and B, which respectively generate therefrom a received signal which is sampled, digitized and stored in block 42 at predetermined sampling instants.

Subsequently, the respective phase difference between the received signals of the two transducers is determined in block 44 for the sampling times. Depending on the distance 30 of the two transducers A and B, however, an ambiguity occurs. This is in Fig. 5 shown in detail.

Fig. 5 shows a schematic representation of an incident on the transducers A and B sound wave front 64. If the distance 30 of the two transducers is greater than half the wavelength λ of the received sound wave front 64, it comes to ambiguities. This means the determined phase difference of the received signals between transducers A and B is ambiguous and thus provides, depending on the distance 30 of the transducers, a number of ambiguous path differences Δx ₁ , Δ ₂ , Δx ₃ .

In this exemplary embodiment according to Fig. 5 Δx ₃ corresponds to the true retardation of the received signals between the transducers A and B. This retardation Δx ₃ provides an associated receiving angle in connection with the distance 30 of the transducers.

In block 46 according to Fig. 4 For the previously determined phase differences, all ambiguous gait differences are calculated. Thereafter, for the respective path differences in a further block 48, all the angles of incidence resulting from these path differences are calculated, from which the associated incidence coordinates are determined in block 50. For each incidence coordinate the sampling time as well as the position or plumbing is stored.

Subsequently, in block 52, the counting variable i is increased by one value and in the further block 54 it is checked whether the counting variable has reached the value N for the number of plumbs to be carried out. If this is not the case, the system jumps back in a loop to the instruction in block 40 in order to determine the impact coordinates for a next plumbing from a further position. However, if the count variable i has reached the value N, a data density about the incidence coordinates is determined in block 56. The data density is a measure of the number of previously collected data within a predetermined range including the respective impact coordinate.

The data density is determined for a plurality of N plumbs and for all sampling times of these plots considered and for each of the ambiguous incident coordinates. In block 58, a maximum data density is determined from this. At a maximum, the impact coordinate at which the data density is greatest is output as valid and for the determination of the soil profile 60. All other ambiguous landing coordinates at this sampling instant are marked invalid in block 62 and discarded.

Fig. 6 shows a block diagram for explaining the apparatus for carrying out the method according to the invention according to Fig. 4 ,

The transducers A and B deliver to the N plummings in each case an electrical received signal 70 ₁ , 70 ₂ ,..., 70 _N or 72 ₁ , 72 ₂ ,..., 72 _N whose further signal processing for the N plumbing according to the blocks 74 ₁ , 74 ₂ , ..., 74 _N takes place.

The further description of the block 74 is based on the first Lotung. The explanations also apply to the other two to N lotions.

The received electrical signals 70 ₁ and 72 _{1 of} the transducers A and B are sampled and digitized in block 76 ₁ at predetermined sampling times.

In the calculation unit 78 ₁ , both the phase difference between the signals 70 ₁ and 72 ₁ and the propagation time of these signals are determined for a plurality of sampling times.

In a further calculation unit 80 ₁ , the previously determined phase differences for the sampling times, as previously described with reference to FIG Fig. 5 explained, the associated ambiguous gait differences determined. For these ambiguous gait differences, the associated ambiguous angles of incidence and incidence coordinates on the soil profile are calculated in a further calculation unit 82 ₁ for the sampling times by means of the signal propagation times and the receiving angle.

In this way, the ambiguous impact coordinates on the soil profile are determined for a plurality of sampling times and for N plumbing. These ambiguous incident coordinates of the N plumbs are passed to a further calculation unit 84 together with the information of the associated sampling times. There is for each sampling time, for each of the N Lotungen and for each of the ambiguous landing coordinates determines a data density in a predetermined area including the landing coordinate. The data density is a measure of the number of data collected within this area. However, the impact coordinates of the same plumb line are not taken into account when determining the density.

This predetermined area is preferably a surface element whose size is small enough and determined depending on the computational effort. However, it is the same for all impact coordinates.

A maximum detector 86 determines the maximum data density for the sampling instants. At each sampling instant, the incident coordinate whose associated area element has a maximum data density is marked as valid and thus corresponds to the true ground point (x, y, z). The other ambiguous landing coordinates are marked as invalid.

The incident coordinate (x, y, z) is composed as follows: the x-coordinate can be determined at each sampling time by means of the laws of trigonometry, the y-coordinate is dependent on the width 26 of the transmitting team 22 and the z-coordinate corresponds the height h calculated from the transit time difference between transducers A and B.

In this case, the coordinate system is related to the vessel 2 or to the transmission and reception arrangement 4. It is also possible to use an absolute coordinate system for carrying out the method, if this is taken into account accordingly in the signal processing.

The method described above may be modified such that a transducer array is used instead of two individual transducers as the receiving arrangement. The receiving arrangement is followed by a direction former or beamformer, which delays the received signals of the converters and adds them to group signals, so that a fan of directional characteristics or beams is clamped in the underwater area. The horizontal one Width of a beam is determined by its horizontal opening angle. This allows a higher resolution in the y direction, in the event that a sufficiently large bundling of the transmission team is not possible.

All mentioned in the above description of the figures, the claims and the introduction of the description features are used individually as well as in any combination with each other. The invention is thus not limited to the described or claimed feature combinations. Rather, all feature combinations are to be regarded as disclosed.

Claims (10)

1. A method for measuring a bottom profile (6) with a transmitting arrangement (20) attached to a water vehicle (2) for the directed emitting of sound signals into an underwater area (8) and with a receiving arrangement (28) attached to this water vehicle (2) with at least two converters for receiving the sound waves reflected from the bottom profile (6) inside the underwater area (8) from which sound waves the converters generate a received signal (70; 72) that is scanned at certain scanning times, digitized and stored (42),
   characterized in that
   a sound signal is successively emitted (40) into the underwater area (8) by the transmitting arrangement (20) with a plurality of N soundings from predetermined positions (P₁, P₂, P₃, P₄, ..., P_N) with aspect angles (ϕ_N) and distances (r_N) to the bottom profile (6) that are different from each other, and whose components of the N soundings which components are reflected from the bottom profile (6) are received (42) by the receiving arrangement (28),
   a phase difference (44) and also the resulting phase differences (46) of the received sound waves between two converters of the receiving arrangement (28) are determined for a plurality of the scanning times and for the N soundings from the received signals (70; 72),
   associated angles of incidence (48) and their coordinates of incidence are determined (50) for these scanning times and for the N soundings to the phase differences,
   a data density in a predetermined area containing the particular coordinates of incidence is determined (56) for these scanning times and for the N soundings to the coordinates of incidence, whereby the data density represents a measure for the number of the previously taken data inside this area,
   the area is selected by a maximum detector (86) in which area the data becomes maximum and the coordinate of incidence belonging to this area is used for determining the bottom profile (6).
2. The method according to claim 1,
   characterized in that
   the receiving arrangement (28) consists of two individual electroacoustic and/or optoacoustic converters that are arranged at a distance (30) greater than one half the wavelength (λ) of the received signal (70; 72).
3. The method according to claim 1,
   characterized in that
   the receiving arrangement (28) consists of a plurality of electroacoustic and/or optoacoustic converters and that the sound waves are received in a directionally selective manner.
4. The method according to one of the previous claims,
   characterized in that
   the areas that contain the coordinates of incidence and are used for determining the data density correspond to area elements with a predetermined size.
5. The method according to one of the previous claims,
   characterized in that the
   predetermined positions (P₁, P₂, P₃, P₄, ..., P_N) of the N soundings are achieved by a forward movement of the transmitting and receiving arrangement (4).
6. A device for measuring a bottom profile (6) with a transmitting arrangement (20) attached to a water vehicle (2) for the directed emitting of sound signals into an underwater area (8) and with a receiving arrangement (28) attached to this water vehicle (2) with at least two converters for receiving the sound waves reflected from the bottom profile (6) inside the underwater area (8) from which sound waves the converters generate a received signal (70; 72) that can be scanned at certain scanning times, digitized and stored (42),
   characterized by
   a transmitting arrangement (20) for the sequential emitting (40) of the sound signal with a plurality of N soundings from predetermined positions (P₁, P₂, P₃, P₄, ..., P_N) with aspect angles (ϕ_N) and distances (r_N) to the bottom profile (6) that are different from each other into the underwater areal (8),
   a receiving arrangement (28) for the particular receiving (42) of the components of the N soundings of the sound signal which components are reflected from the bottom profile (6),
   two calculating units (78; 80) for determining, for a plurality of the scanning times and for the N soundings, a phase difference (44) as well as the resulting phase differences (46) of the received sound waves between two converters of the receiving arrangement (28),
   another calculating unit (82) for determining angles of incidence (48) associated with the phase differences and for determining the particular coordinates of incidence (50) from the angles of incidence for these scanning times and for the N soundings,
   another calculating unit (84) for determining a data density (56) of the coordinates of incidence for these scanning times and for the N sounding in a predetermined area containing the particular coordinates of incidence, whereby the data density represents a measure for the number of previously determined data inside this area,
   a maximum detector (86) for selecting the area in which the data density becomes maximum and for determining a coordinate of incidence (60) of the bottom profile (6) which coordinate belongs to this area.
7. The device according to claim 6
   characterized in that
   the receiving arrangement (28) consists of two individual electroacoustic and/or optoacoustic converters that are arranged at a distance greater than one half the wavelength (λ) of the received signal (70; 72).
8. The device according to claim 6
   characterized in that
   the receiving arrangement (28) consists of a plurality of electroacoustic and/or optoacoustic converters with which the sound waves can be received in a directionally selective manner.
9. The device according to one of claims 6 to 8
   characterized in that
   the areas that contain the coordinates of incidence and are used for determining the data density are area elements with a predetermined size.
10. The device according to one of claims 6 to 9
    characterized in that
    the predetermined positions (P₁, P₂, P₃, P₄, ..., P_N) of the N soundings can be achieved by a forward movement of the transmitting and receiving arrangement (4).

Images